Molecular Cloning and Sequence of a Complementary DNA Encoding 1-Aminocyclopropane-l-carboxylate Synthase Induced by Tissue Wounding

Abstract

1-Aminocyclopropane-l-carboxylate (ACC) synthase [EC 4.4.1.14] is the key enzyme regulating ethylene biosynthesis in higher plants. A complementary DNA encoding wound-induced ACC synthase from mesocarp of winter squash (Cucurbita maxima Duch.) fruits was cloned, and its complete nucleotide sequence determined. The cloned cDNA contained an open reading frame of 1479 base pairs encoding a sequence of 493 amino acids. Identification of the cDNA was accomplished by expression of active enzyme in Escherichia coli harboring the cDNA and by the presence of a partial amino acid sequence identical to that found in the purified enzyme. A putative pyridoxal phosphate binding site of the enzyme is suggested. Northern blot analysis showed that the ACC synthase gene was activated by tissue wounding, and its expression was repressed by ethylene. Genomic Southern analysis indicates the presence of at least another sequence which weakly hybridizes with the cDNA.